This invention relates in general to electrophotographic imaging members and, more specifically, to electrophotographic imaging members comprising a shallow trap dopant and processes for fabricating the members.
Electrophotographic imaging members (photoreceptors) are well known. Typical electrophotographic imaging members are commonly utilized in electrophotographic (xerographic) processes in either a flexible belt or a rigid drum configuration. These electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive or charge generating layer (CGL) which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer (CTL). Generally, where the two electrically operative layers are supported on a conductive layer, the charge generating layer is sandwiched between a contiguous charge transport layer and the supporting conductive layer. Alternatively, the charge transport layer may be sandwiched between the supporting electrode and a charge generating layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a member such as paper.
One problem with prior art photoreceptors relates to photoinduced discharge curve (PIDC) characteristics of the photoreceptors. The expression photoinduced discharged curve (PIDC), as employed herein, is defined as a relationship between the potential as a function of exposure and is a measure of the sensitivity of the device. It generally represents the supply efficiency (number carriers injected from the generator layer into the transport layer per incident photon) as a function of the field across the device. More specifically, when the V.sub.low, voltage at a high light exposure, is below a predetermined value, the imaging system consumes toner too rapidly, resulting in early failure of the imaging system. This is due to excess deposition of toner in the image areas to form very dense layers. V.sub.low is related to V.sub.residual. The combination of electrical bias and V.sub.low results in overtoning during electrostatic latent image development to form toner images that are too dense, i.e., the electrical development field is too large. "V.sub.low ", as employed herein, is defined as the surface potential of a PIDC at a high intensity light exposure of, e.g., about 2.5-15 ergs/cm.sup.2. "V.sub.residual ", as employed herein, is defined as the surface potential of a PIDC at a given light exposure (e.g., about 25-300 ergs/cm.sup.2), that is significantly higher (e.g., about 10 times) than the exposure leading to V.sub.low. Cyclic stability is important and V.sub.residual and V.sub.low can increase with cycling due to persistently trapped charges. V.sub.low approaches V.sub.residual in an infinite amount of time. Thus, it is desirable to raise V.sub.low in a controlled fashion to a desirable value, which can be maintained under repeated use, and preferably without significantly altering the initial and low exposure photosensitivity. In other words, a more tunable photoreceptor is desirable. Tunable photoreceptors, due to their tunable photosensitivity characteristics, have the advantage of being applicable to many different xerographic machines, including printers, copiers, duplicators, facsimile machines, multifunctional machines, and the like. With dual photoconductive components in a charge generating layer, a high sensitivity pigment such as hydroxygallium phthalocyanine and a low sensitivity pigment such as alkylhydroxygallium phthalocyanine, the initial photosensitivity can be adjusted within a range corresponding to the loading ratio of each component. However, it is often difficult to match both high field and low field photoinduced discharge curves (V.sub.low PIDC) by merely adjusting the CGL composition. V.sub.low is related to charge generation and transport and can be adjusted by photogeneration and charge transport efficiencies. V.sub.low, is a critical parameter to toner consumption and is difficult to adjust by merely varying the composition of a charge generation layer. For example, a multilayered photoreceptor comprising a charge generating layer of chlorogallium phthalocyanine dispersed in a film forming binder and a charge transport layer comprising an arylamine charge transport material in a film forming binder has a low V.sub.low, and attempts to raise V.sub.low by lowering the photogeneration efficiency by changing the CGL composition is not sufficient because it may also change the initial photosensitivity to some undesirable value.